A battery

Abstract

The application provides a battery, in particular a high-safety battery. The application optimizes the percentage of the area of hot-melt double-sided adhesive tape to the area of a bare battery cell and the percentage of a carbonate solvent in electrolyte to the total mass of organic solvents in electrolyte, ensures that the electrolyte has the best performance, reduces the influence of the carbonate solvent on the swelling of the hot-melt double-sided adhesive tape, and maintains the viscosity of the hot-melt double-sided adhesive tape; meanwhile, the compound shown in formula I is added to the electrolyte, which can not only form a dense and stable interface film at the negative electrode, but also can occur polymerization reaction to absorb heat and reduce the temperature of the system when the temperature in the battery increases, thereby reducing the risk of thermal runaway and further improving the safety performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a battery, and more particularly to a high-safety lithium ion battery. BACKGROUND

[0002] With the attention paid to the exhaustion of non-renewable energy and environmental pollution, renewable clean energy has rapidly developed. Among them, lithium ion batteries have the characteristics of high energy density, long cycle life, low self-discharge rate, environmental friendliness, etc., and are widely used in consumer electronics, new energy power vehicles and other power battery products.

[0003] With the continuous expansion of the application field of lithium ion batteries, people's requirements for the safety performance of lithium ion batteries are continuously improved, and the development of higher safety lithium ion batteries is one of the main demands of the market. Large rate charging and discharging, overcharging and overdischarging, high temperature, etc. may cause the surface temperature of the lithium ion battery to rise in a short time, intensify the side reaction to continue to produce heat, and the internal temperature to increase sharply, leading to thermal runaway and causing safety accidents; impact, drop, etc. can easily cause the internal diaphragm of the battery cell to be folded, causing a short circuit, and accidents such as fire and explosion may occur. The general lithium ion battery bare cell is wrapped with an aluminum plastic film, and a hot melt double-sided adhesive is attached between the bare cell and the aluminum plastic film. The hot melt double-sided adhesive will melt under heat pressure, and then tightly bond with the outer aluminum plastic film, well fixing the position of the bare cell in the aluminum plastic film, preventing the bare cell from moving in the aluminum plastic film during the drop test, and avoiding the folding of the diaphragm of the bare cell, which may cause a short circuit of the battery. Therefore, the adhesion of the hot melt double-sided adhesive directly affects the pass rate of the drop test and the safety performance of the battery. SUMMARY

[0004] In order to solve the safety problem of fire and explosion caused by the rapid rise of temperature or accidental drop of the battery during use, the present application optimizes the percentage of the area of the hot melt double-sided adhesive to the area of the length and width of the bare cell and the percentage of the carbonate solvent in the total mass of the organic solvent in the electrolyte, ensures that the electrolyte performs optimally while reducing the swelling of the hot melt double-sided adhesive by the carbonate solvent, and maintains the adhesion of the hot melt double-sided adhesive. At the same time, a compound represented by formula 1 is added to the electrolyte, which not only forms a dense and stable interface film at the negative electrode, but also absorbs heat and reduces the risk of thermal runaway when the internal temperature of the battery rises, thereby further improving the safety performance of the battery.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] A battery, comprising a bare cell, a hot melt double-sided adhesive and an electrolyte; the hot melt double-sided adhesive is arranged on the length and width of the bare cell; the electrolyte comprises a lithium salt, an organic solvent and an additive, and the organic solvent comprises at least one carbonate solvent.

[0007] The battery satisfies the following conditions:

[0008] 0.5≤A / B≤2

[0009] wherein A is the percentage of the area of the hot-melt double-sided tape to the area of the length-width surface of the bare battery cell, and B is the percentage of the mass of the carbonate solvent to the total mass of the organic solvent in the electrolyte.

[0010] According to the embodiments of the present application, A / B is 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or any point value in the range consisting of any two of the above endpoints. When A / B < 0.5, i.e., the percentage of the area of the hot-melt double-sided tape to the area of the length-width surface of the bare battery cell is small, it cannot effectively fix the bare battery cell, and the safety performance of the battery (drop pass rate) is reduced; or, the percentage of the mass of the carbonate solvent to the total mass of the organic solvent in the electrolyte is high, which makes the swelling of the hot-melt double-sided tape large and the viscosity of the electrolyte system high, affecting the safety performance and electrochemical performance of the battery. When A / B > 2, i.e., the percentage of the area of the hot-melt double-sided tape to the area of the length-width surface of the bare battery cell is large, which seriously affects the infiltration of the electrolyte to the bare battery cell, resulting in a decrease in residual liquid amount and deterioration of the high-temperature cycle performance of the battery; or, the percentage of the mass of the high-boiling point carbonate solvent to the total mass of the organic solvent in the electrolyte is low, which deteriorates the high-temperature cycle and safety performance (hot box pass rate) of the battery. Therefore, the ratio is controlled to be 0.5≤A / B≤2.

[0011] According to the embodiments of the present application, 0.05≤A≤0.9, for example, A is 0.05, 0.1, 0.15, 0.20, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.80, 0.85, or 0.9. When 0.05≤A≤0.9, it is avoided that the percentage of the area of the hot-melt double-sided tape to the area of the length-width surface of the bare battery cell is small, which cannot fix the bare battery cell and reduces the safety performance of the battery; it is also avoided that the percentage of the area of the hot-melt double-sided tape to the area of the length-width surface of the bare battery cell is large, which affects the infiltration of the electrolyte to the bare battery cell, resulting in a decrease in residual liquid amount and deterioration of the high-temperature cycle performance of the battery.

[0012] According to an embodiment of the present invention, 0.20≤B≤0.80, for example, B is 0.20, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, or 0.80. When B < 0.2, the percentage of the mass of the carbonate solvent to the total mass of the organic solvent in the electrolyte is too small, and the high-temperature cycle performance and hot box pass rate of the battery cannot be guaranteed; when B > 0.8, the percentage of the mass of the carbonate solvent to the total mass of the organic solvent in the electrolyte is too high, which has a serious swelling effect on the hot melt adhesive and reduces safety performance. In addition, the viscosity of the electrolyte system is too high, which deteriorates the electrical performance. Therefore, 0.20≤B≤0.80 is controlled.

[0013] According to an embodiment of the present invention, the bare cell includes a positive electrode sheet, a negative electrode sheet and a separator.

[0014] According to an embodiment of the present invention, the bare cell is a laminated bare cell formed by stacking a positive electrode sheet, a negative electrode sheet and a separator; or, the bare cell is a wound bare cell formed by winding a positive electrode sheet, a negative electrode sheet and a separator.

[0015] According to an embodiment of the present invention, the battery further includes a shell, and the shell is used to encapsulate the bare cell.

[0016] According to an embodiment of the present invention, a shell is provided on the outer side of the hot-melt double-sided adhesive, that is, the hot-melt double-sided adhesive is provided between the bare battery cell and the shell.

[0017] According to an embodiment of the present invention, the shell is a composite film material comprising at least three layers, the innermost layer is polyethylene and / or polypropylene with good heat sealing properties and resistance to electrolyte corrosion, the middle layer is aluminum foil with good resistance to water vapor, air and acid corrosion, and the outermost layer is a multi-layer film layer.

[0018] According to an embodiment of the present invention, the housing is, for example, an aluminum-plastic film, for example, an aluminum-plastic film of model DNP153 purchased through commercial channels.

[0019] According to an embodiment of the present invention, the thickness of the shell is 65 μm to 250 μm.

[0020] According to an embodiment of the present invention, the thickness of the hot melt double-sided adhesive is 4 μm to 20 μm.

[0021] According to an embodiment of the present invention, the hot melt double-sided adhesive includes a high melting point base film and a hot melt material, and the hot melt material is arranged on both sides of the high melting point base film; the high melting point base film is at least one of polytetrafluoroethylene, polyester, polyimide, polyethylene, and polypropylene, and the hot melt material is at least one of modified polypropylene and modified polyethylene.

[0022] According to an embodiment of the present application, the long and wide surface refers to a surface on which the length and width of the bare battery cell are located.

[0023] According to an embodiment of the present application, the positive active material in the positive electrode sheet is at least one of lithium manganate, lithium iron phosphate, lithium nickel cobalt manganate ternary material, lithium nickel manganate, and lithium-rich manganese-based material.

[0024] According to an embodiment of the present application, the negative active material in the negative electrode sheet is at least one of artificial graphite, natural graphite, hard carbon, soft carbon, mesocarbon microbeads, silicon-based negative electrode material, and lithium-containing metal composite oxide material.

[0025] According to an embodiment of the present application, the lithium salt is at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bisfluorosulfonimide, lithium bis-trifluoromethanesulfonimide, lithium bisoxalate borate, and lithium difluoro oxalate borate.

[0026] According to an embodiment of the present application, the mass percentage of the lithium salt in the total mass of the electrolyte is 12wt% to 18wt%.

[0027] According to an embodiment of the present application, the carbonate-based solvent is selected from propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and fluoroethylene carbonate.

[0028] According to an embodiment of the present application, the organic solvent further includes at least one of the following compounds: γ-butyrolactone, sulfolane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate.

[0029] According to an embodiment of the present application, the mass percentage of the organic solvent in the total mass of the electrolyte is 10wt% to 80wt%.

[0030] According to an embodiment of the present application, the additive includes a first additive selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), diethyl sulfate (DTD), 1,3-propane sulfone (PS), ethylene sulfite (ES), tris(trimethylsilyl)borate (TMSB), and tris(trimethylsilyl)phosphate (TMSP).

[0031] According to an embodiment of the present application, the additive further includes a second additive selected from at least one of the compounds shown in Formula 1:

[0032]

[0033] wherein R1, R2, R3, R4are the same or different and independently of each other selected from halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, substituted or unsubstituted alkynyl, and at least one of R1, R2, R3, R4is selected from substituted or unsubstituted alkenyl or substituted or unsubstituted alkynyl; and if substituted, the substituents are halogen, alkyl.

[0034] According to an embodiment of the present application, R1, R2, R3, R4are the same or different and independently of each other selected from halogen, substituted or unsubstituted C 1-6 alkyl, substituted or unsubstituted C 2-6 alkenyl, substituted or unsubstituted C 2-6 alkynyl, and at least one of R1, R2, R3, R4is selected from substituted or unsubstituted C 2-6 alkenyl or substituted or unsubstituted C 2-6 alkynyl; and if substituted, the substituents are halogen, C 1-6 alkyl.

[0035] According to an embodiment of the present application, R1, R2, R3, R4are the same or different and independently of each other selected from halogen, substituted or unsubstituted C 1-3 alkyl, substituted or unsubstituted C 2-3 alkenyl, substituted or unsubstituted C 2-3 alkynyl, and at least one of R1, R2, R3, R4is selected from substituted or unsubstituted C 2-3 alkenyl or substituted or unsubstituted C 2-3 alkynyl; and if substituted, the substituents are halogen, C 1-3 alkyl.

[0036] According to an embodiment of the present application, the compound of formula 1 is selected from at least one of the following compounds I to IV:

[0037]

[0038]

[0039] According to an embodiment of the present application, the percentage of the mass of the first additive in the total mass of the electrolyte is 0.5wt.%-8wt.%, for example, 0.5wt.%, 0.6wt.%, 0.7wt.%, 0.8wt.%, 0.9wt.%, 1wt.%, 1.2wt.%, 1.5wt.%, 1.8wt.%, 2wt.%, 2.2wt.%, 2.5wt.%, 2.8wt.%, 3wt.%, 3.2wt.%, 3.5wt.%, 3.6wt.%, 3.8wt.%, 4wt.%, 5wt.%, 6wt.%, 7wt.% or 8wt.%.

[0040] According to an embodiment of the present application, the percentage of the mass of the second additive in the total mass of the electrolyte is 0.3wt.%-4wt.%, for example, 0.3wt.%, 0.4wt.%, 0.5wt.%, 0.6wt.%, 0.7wt.%, 0.8wt.%, 0.9wt.%, 1wt.%, 1.2wt.%, 1.5wt.%, 1.8wt.%, 2wt.%, 2.2wt.%, 2.5wt.%, 2.8wt.%, 3wt.%, 3.2wt.%, 3.5wt.%, 3.6wt.%, 3.8wt.% or 4wt.%.

[0041] Advantages of the present application:

[0042] The present application provides a battery, in particular a high-safety battery. By optimizing the percentage of the area of the hot-melt double-sided tape to the area of the bare battery cell and the percentage of the mass of the carbonate solvent in the total mass of the organic solvent in the electrolyte, the present application ensures that the electrolyte performs optimally while reducing the swelling of the hot-melt double-sided tape by the carbonate solvent, maintaining the adhesion of the hot-melt double-sided tape; at the same time, adding a compound represented by Formula 1 to the electrolyte not only forms a dense and stable interface film at the negative electrode, but also absorbs heat and reduces the risk of thermal runaway when the internal temperature of the battery rises, thereby further improving the safety performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 Position diagram of hot-melt adhesive in the battery.

[0044] Figure legend: 1 is the shell, 2 is the bare battery cell, and 3 is the hot-melt double-sided tape. DETAILED DESCRIPTION

[0045] The present application will be further described in detail below with reference to specific examples. It should be understood that the following examples are only illustrative and explanatory of the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology achieved based on the above description of the present application is encompassed within the scope of protection intended by the present application.

[0046] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples are commercially available unless otherwise specified.

[0047] Preparation of lithium ion battery

[0048] (1) Preparation of positive electrode sheet

[0049] The positive electrode active material lithium nickel cobalt manganese oxide (NCM622), the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black were mixed in a weight ratio of 96.5:2:1.5, N-methyl pyrrolidone (NMP) was added, and stirring was performed under the action of a vacuum stirrer until the mixed system became a positive electrode slurry with uniform fluidity; the positive electrode slurry was uniformly coated on an aluminum foil with a thickness of 7 μm; the coated aluminum foil was baked in an oven with 5 different temperature gradients, then dried in an oven at 120°C for 8 h, and then subjected to rolling and slitting to obtain the positive electrode sheet.

[0050] (2) Preparation of negative electrode sheet

[0051] The negative electrode active material artificial graphite, the thickening agent sodium carboxymethyl cellulose (CMC-Na), the binder styrene-butadiene rubber, the conductive agent acetylene black, and the conductive agent single-walled carbon nanotube (SWCNT) were mixed in a weight ratio of 95.9:1:2:1:0.1, deionized water was added, and a negative electrode slurry was obtained under the action of a vacuum stirrer; the negative electrode slurry was uniformly coated on a copper foil with a thickness of 6 μm; and the negative electrode sheet was obtained after drying (temperature: 85°C, time: 5 h), rolling, and die cutting.

[0052] (3) Preparation of electrolyte

[0053] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), EC / DMC / EP / PP were mixed uniformly, wherein the sum of the mass of EC and DMC was equal to the mass percentage B of the carbonic acid ester solvent in the total mass of the organic solvent in the electrolyte, the mass ratio of EC and DMC was 1:1, and the mass ratio of EP and PP was 1:1; 14 wt% of LiPF6 and an additive were quickly added to the mixed solution, and stirring was performed until uniformity to obtain the electrolyte.

[0054] (4) Preparation of separator

[0055] A 9 μm thick coated polyethylene separator was selected.

[0056] (5) Preparation of lithium ion battery

[0057] The prepared positive electrode sheet, the separator, and the negative electrode sheet are wound to obtain a bare cell without liquid injection; a layer of hot-melt double-sided adhesive (high-melting-point base film: polytetrafluoroethylene, hot-melt material: modified polypropylene) is coated on the upper and lower surfaces (surfaces on which the length and width are located) of the bare cell, the bare cell coated with the hot-melt double-sided adhesive is placed in a shell (purchased from Dowling, model number: DNP153) that has been punched, and the electrolyte prepared above is injected into the shell, and the lithium ion battery is obtained through vacuum packaging, standing, formation, shaping, sorting, and other processes.

[0058] The test methods for the high-temperature cycle performance and safety performance of the lithium ion batteries prepared in the examples and comparative examples are as follows:

[0059] (1) Drop test: the battery is placed in a 25°C constant-temperature box, charged to 4.35V at a constant current of 0.5C, and then charged at a constant voltage until the current is 0.05C, the battery is placed in an environment at 25°C, and the battery is dropped from a height of 1 meter onto a concrete floor, 1 battery is repeated for 3 times, and the battery is impacted in each random direction during the drop, if there is leakage, fire, or explosion, it is determined to be invalid, and 10 batteries are tested in each group.

[0060] (2) 55°C cycle test: the obtained battery is placed in an environment at (55±2) °C, and stands for 2-3 hours, when the battery body reaches (55±2) °C, the battery is charged to the upper limit voltage 4.25V at 1C constant current and constant voltage, and the cutoff current is 0.05C, the battery is placed for 5 minutes after being fully charged, and then discharged at 1C constant current to the cutoff voltage 3.0V, the highest discharge capacity of the first 3 cycles is recorded as the initial capacity Q1, when the cycle reaches the required number of times, the last discharge capacity Q2 of the battery is recorded; the recording results are shown in Table 2. The calculation formula used is as follows: capacity retention rate (%) = Q2 / Q1 x 100%.

[0061] (3) Hot box test: the prepared lithium ion battery is placed in a 135°C constant-temperature box for 120 minutes, and whether the battery catches fire or explodes is observed, if it catches fire or explodes, it is determined to be invalid, and 10 batteries are tested in each group.

[0062] Comparative examples 1-8 and examples 1-8

[0063] The additives of comparative examples 1-8 and examples 1-8 are 1wt% of vinylene carbonate based on the total mass of the electrolyte, 1wt% of fluoroethylene carbonate based on the total mass of the electrolyte, 2wt% of ethylene sulfate based on the total mass of the electrolyte, and 2wt% of 1,3-propane sulfone lactone based on the total mass of the electrolyte.

[0064] Table 1 battery composition and performance test results of comparative examples 1-8 and examples 1-8

[0065]

[0066] From the test results of Comparative Examples 1-8 and Example 1-8, it can be seen that in the range of 5%≤A≤90%, 0.5≤A / B≤2, the lithium ion battery has the best performance, because the hot melt adhesive area ratio is too small, and the adhesion effect cannot be achieved, and the hot melt adhesive area is too large, and the carbonate solvent content is relatively small, that is, the A / B value is large, which seriously affects the cell body infiltration, resulting in a decrease in residual liquid amount and poor high temperature cycle.

[0067] From the test results of Comparative Examples 1-8 and Example 1-8, it can be seen that in the range of 20%≤B≤80%, 0.5≤A / B≤2, the lithium ion battery has the best performance, because the percentage content of high-boiling-point carbonate solvent is too small, which deteriorates the high-temperature cycle and hot-box pass rate, and the percentage content of carbonate solvent is too large, that is, the A / B value is small, which increases the hot melt adhesive swelling, reduces the drop pass rate, and also causes the electrolyte system viscosity to be too large, which is not conducive to the cycle performance.

[0068] Examples 9-14

[0069] The additives of Examples 9-14 are 1wt% of vinylene carbonate based on the total mass of the electrolyte, 1wt% of fluoroethylene carbonate based on the total mass of the electrolyte, 2wt% of ethylene sulfate based on the total mass of the electrolyte, 2wt% of 1,3-propane sulfone lactone based on the total mass of the electrolyte, and a compound represented by Formula 1.

[0070] Table 2 Battery composition and performance test results of Examples 9-14

[0071]

[0072] From Comparative Examples 1-8 and Examples 7, 9-14, it can be seen that when the compound represented by Formula 1 is introduced into the electrolyte, the battery hot-box pass rate can be significantly improved, and the battery exhibits good safety performance.

[0073] The above describes embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A battery, characterized by, The battery comprises a bare battery cell, a hot melt double-sided adhesive and an electrolyte; the hot melt double-sided adhesive is arranged on the length-width surface of the bare battery cell; the electrolyte comprises a lithium salt, an organic solvent and an additive, and the organic solvent comprises at least one carbonate solvent; The battery satisfies the following conditions: 0.5≤A / B≤2 Wherein, A is the percentage of the area of the hot melt double-sided adhesive to the area of the length-width surface of the bare battery cell, and B is the percentage of the mass of the carbonate solvent to the total mass of the organic solvent in the electrolyte; 0.05≤A≤0.90; 0.20≤B≤0.

80. The hot melt double-sided adhesive comprises a hot melt material, and the hot melt material is at least one of modified polypropylene and modified polyethylene. The carbonate solvent is at least one of propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and fluoroethylene carbonate.

2. The battery of claim 1, wherein, The outer side of the hot melt double-sided adhesive is provided with an outer shell, i.e., the hot melt double-sided adhesive is arranged between the bare battery cell and the outer shell, and the outer shell is a composite film material comprising at least three layers, the innermost layer is polyethylene and / or polypropylene, the middle layer is an aluminum foil, and the outermost layer is a multilayer film layer.

3. The battery of claim 1, wherein, The hot melt double-sided adhesive further comprises a high-melting-point base film, and the hot melt material is arranged on both sides of the high-melting-point base film; the high-melting-point base film is at least one of polytetrafluoroethylene, polyester, polyimide, polyethylene and polypropylene.

4. The battery of claim 1, wherein, The additive comprises a first additive, and the first additive is at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), diethyl sulfate (DTD), 1,3-propane sulfonate (PS), ethylene sulfite (ES), tris(trimethylsilyl)borate (TMSB) and tris(trimethylsilyl)phosphate (TMSP).

5. The battery of claim 1, wherein, The additive further comprises a second additive, and the second additive is at least one of the compounds shown in Formula 1: Formula 1 Wherein, R1, R2, R3 and R4 are the same or different, and are independently selected from halogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl and substituted or unsubstituted alkynyl, and at least one of R1, R2, R3 and R4 is selected from substituted or unsubstituted alkenyl or substituted or unsubstituted alkynyl; if substituted, the substituent is halogen or alkyl.

6. The battery of claim 4, wherein, The percentage of the mass of the first additive to the total mass of the electrolyte is 0.5wt.%-8wt.%.

7. The battery of claim 5, wherein, The percentage of the mass of the second additive to the total mass of the electrolyte is 0.3wt.%-4wt.%.

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